The present invention relates to a device and method for reducing the consumption of urea and/or hygroscopic chemical substances in paste materials for printing cotton and viscose fabrics.
In the fabric printing field there are already known several types of steaming chambers, into which the fabric, after having being printed, is introduced in order to set the printed pattern.
Prior steaming chambers, however, are affected by several drawbacks, the main of which is that they require that comparatively great amounts of urea be used, with a consequent great pollution of the used water.
Also known is the fact that cotton and viscose fabrics are conventionally printed by using reactive coloring materials or dyes.
In order to set, under a steam environment, these dyes, urea must be added to the printing paste material, with a proportion of about 150 g per Kg.
This urea is required in order to absorb water present in the processing steam, so as to cause the cellulose fibres to be swollen.
Moreover, urea facilitates the absorption of the dye material as well as its chemical reaction with the fibres to be dyed.
As urea is dissolved in the processing steam, an endothermic reaction will occur causing the printed fabric to be quickly cooled.
This reaction will cause further steam to condense, so as to enhance the moisture contents of the printed fabric, thereby promoting the above mentioned setting process.
To the foregoing it is to be moreover added that from urea ammonia is evolved which pollutes air to which steam is discharged or the water used in a fabric washing step following the steam setting step thereof.
In this connection it should be moreover pointed out that present anti-pollution rules are very restrictive and, accordingly, it would be advantageous to greatly reduce the use of urea in fabric printing paste materials.
Such an use, as it should be apparent, could be greatly reduced if the moisture contents of the fabric material were increased as this fabric is supplied to the steaming chamber.
In actual practice, in order to heat water up to its boiling point, it is necessary to use an amount of energy which corresponds to three times the energy amount required to bring to 100.degree. C. the fabric.
This means that a greater amount of steam will tend to condense on a fabric having a higher moisture content, independently from the amount of urea which is present.
Attempts performed in order to increase the moisture rate of the printed fabric material provided for moistening the fabrics before steaming them.
Some prior systems provided for spraying atomized water directly on the printed fabric, supplied in a not set condition.
However, these systems did not provide satisfactory results and they can operate in a reliable way exclusively if they are controlled by sophisticated and expensive control systems, since water absorption by the fabric is very uneven with the danger of adding an excessive water amount to some regions of the fabric piece and a low water amount to other regions thereof.